If that's about 7ft long I have 6 hens in an ark type coop that length, and when they are in a row on the perch there is no room for anyone else! The nest box area is separate and not really big enough. I've an Eglu they claim would take 4, but even with a run extension 3 is enough.And a small garden shed which houses 6 and a cockerel with a home made run. The ark is in a bought dog run.
Not sure if that helps. I think I would err on the side of less. 6 ex batts is a lot of eggs, and then when they grow old its a lot of geriatric chicken and no eggs
And then you can get more, because acquiring chickens is addictive

btw i am not really doing it for the eggs - i only use them for baking - so most will be given away - the idea is really a retirement home for ex bats

I have a disabled one Hence the eye wateringly expensive eglu as she can't manage ramps or steps. I was going to wring her neck, but so glad I didn't. She has such a personality, and has had a very happy 6 months so far. And lays an egg on alternate days

awww that is sweet - allotmenters have said about how to get rid of if they don't lay

hopefully they gonna be happy and lay as and when they feel like they want to - no neck wringing for my little henrietta (name suggested by one of the p-taking allotmenters when i said i don't mind if they lay

a coop that size will seem huge to ex bats especially with a run as well.

it could take 10 but as a couple will probably die quite soon that would give 8 which would be comfy and far bigger that they were used to.
a couple more might well pop off during the laying season making it roomy for 6 (an ideal number of fairly small chooks for that space) .

you then have the choice of getting a few more and picking up the originals as they pop off over the next year or so
or
getting a couple of gallons of soup from the survivors when they go out of lay in the autumn,thoroughly cleaning the coop,moving the run and starting a new batch of ten.
i would favour the latter, they will have had a nice retirement , they get a kind end rather than getting ill or suffering the old chook things, they wont infect the next ones with anything or fight with them ( introducing new birds to an existing flock is a bit of an art form if one is to avoid unpleasantness) and you get a few very good "stock cubes".

it might seem rather brutal but battery hens are short lived critters and unlike some of the old breeds dont really do old age as matriarchs.

lps when building your pen think vermin as foxes can climb and dig so a roof is a good idea as is pegging/slabbing at least a couple of feet of netting to the ground outside the fence line ,rats n stoats etc are also an issue but require a different approach.
a pen that is easily dismantled and moved is sensible as rotating the ground is not only good for the birds health but good for growing stuff as well .
the frass from under the perching area is ace in a mixture tub but needs either that or composting (avoid too much leaching with a cover to keep rain off) , if used directly in the "raw" state as a plant feed it is a bit harsh on roots.

i have been thinking of laying under the whole coop and winter run area in wire and roofing it in exterior plywood

- however the internet seems to suggest it is better to lay the wire are a 90 degree angle at floor level and about 45 degrees at top - i really do not like the idea of an open top run as foxes are a big problem on the allotment and a few people have lost loads of chicken - and i do not want to add to this

the advantage of a ply roof is that they keep dry they donít like cold rain and mud is bad for their feet (and various other damp related problems).

a wire roof can be fox proof .
the 90 degree outwards along the floor does make the wire last longer than digging it into a trench,it is easier to move and if it is well held down tis more than a nights digging to get in ( a few inches into a slot is no great problem to radjel.)

the other advantage of a roof is that with open pens you will probably get very plump sparrows and pigeons (at your expense ) and the flock is more exposed to wild bird pests and diseases.

Doing the 90 degree outwards along ground will save me a good few metres of wire - and a fair bit of time - so win-win. I just don't understand why it is the fox proof chosen option rather than wire laid under the who hen coop and pen area.

I may put some pics up tonight and show what i have done so far - as it has come along people have added ideas of what to do so it is ever evolving (improving)

Having once kept ex-bats they did OK as free range on a sunny day, but stared miserably out of the door whenever it rained. So roof is a good idea for wet weather, but if they can get some sun too they'll love it.

One in particular was a great character - in the habit of pecking our toes when we wore open sandals.

Wire as a "floor" under the whole pen is good until it rusts, or gets buried completely, or catches your shovel corner as yu muck out...

I found wire on the floor was a bad idea for the same reasons. I had a small run originally built for bunnies with a wire floor. I used it for my broody hens to keep their babes in when too small for general population. chickens as you know like to scratch for food
one got its foot caught in the hoop of wire.
also they poop on it and it rusts quickly.

sadly foxes will be a problem no matter what you do to keep them out. an allotment must seem like a fast food restaurant for them. waste fruit and veg and chickens to boot.
shutting them into the house at night has kept my chickens safe.
touch wood!

I got a huge chuck of the coop done this weekend - and did a 13ft (4m) side of the run - with a 60cm 90 degree (doubled because I am sceptical and think maybe there is a bigger more agile devil fox out there with superpowere Loads of work and aching arms now but I was pleased with the result

BUT after coming home and reading the comments, I am worried again - maybe I should have the whole area covered in chicken wire (the idea was to cover the wire 3-4 inches of earth)

so now i am thinking of covering the night/winter pen in concrete slabs instead - i have research and it seems that 30cm of wire turned out is sufficient, but what if it is a really determined fox?